Capping processes for plastic containers typically require the upper portion of the container, such as the neck finish, to meet exacting dimensional tolerances. To achieve the necessary tolerances, the upper portions of the containers are usually produced using injection molding processes, for example, by injection blow molding the containers. Injection blow molding processes are at a significant output-to-cavity disadvantage, however, when compared to other types of blow molding, such as extrusion blow molding. In addition, injection blow molding often requires expensive injection manifolds and involves sensitive injection processes.
According to another method of making containers, a preform with a pre-configured upper portion (e.g., neck finish) is made by injection molding. Subsequently, a container is blow molded from the lower portion of the preform. The upper portion can become distorted during blow molding, however, due to the heat applied to the preform. This can cause the pre-configured upper portion to fall out of tolerance.
The process of extrusion blow molding plastic containers typically involves the steps of extruding a tube of monolayer or multilayer plastic material, capturing the tube between opposed mold sections, blowing the tube to the contours of the mold cavity, opening the mold, removing the container, and trimming the end of the container neck finish. This trimming operation can involve removal of a flash or moil from the neck finish. The trimmed material may be scrapped or, alternatively, recycled as process regrind.
In another exemplary extrusion blow molding operation, the trimming operation can involve separation of two containers that are molded end-to-end. In either case, the trimming operation can leave an uneven end surface for later sealing engagement with a container closure. Furthermore, the end surface of the container neck finish may have mold parting line seams that can deleteriously affect sealing engagement with a container closure. These uneven or inconsistent end surface features can also affect induction sealing. Induction sealing can typically involve induction welding a metallic liner disk to a container end surface after filling the container to obtain a satisfactory container seal.
In order to address these disadvantages, it has been proposed to burnish the end surface of the container neck finish by contacting the neck finish end surface with a heated burnishing tool. Upon contacting the container neck finish end surface, the tool simultaneously heats the end portion of the neck finish to a particular softening temperature of the plastic material and modifies the end surface to eliminate mold parting line seams, uneven trim portions, and other post-molding imperfections. This process also has certain disadvantages.
For example, the heated plastic of the container neck finish may tend to stick to the heated burnishing tool. It is also difficult to control the temperature of the burnishing tool so as to obtain a desired temperature at the burnishing surface of the tool. Moreover, effective burnishing often requires that one of the container or the burnishing tool be rotated relative to the other to achieve a desired effect. Such rotation introduces additional process variables and, consequently, affects production speed. Thus, the tendency of the heated plastic to stick to the burnishing tool, in combination with the oft-required rotational step and difficulty of controlling the burnishing surface temperature of the tool, makes it difficult to determine and control the optimum tool-to-surface contact time (i.e., dwell time). The dwell time, during which the burnishing tool is in contact with the end portion of the neck finish, as well as additional process variables, should be minimized to achieve desired production speeds. Regardless, in many applications, burnishing is unable to manipulate sufficient plastic to achieve practical production cycle times.
Another proposed solution to the disadvantages outlined above is to reform the neck finish after the container is initially formed. In this solution, the container is heated to soften the portion of the container that requires reforming and then a tool is brought into contact with the softened portion. Typically, heat is applied using infrared (IR) heat lamp tunnels or heater bands. IR radiation is electromagnetic radiation whose wavelength is longer than that of visible light (400-700 nm), but shorter than that of terahertz radiation (100 μm-1 mm) and microwaves (about 30,000 μm). Infrared radiation spans roughly three orders of magnitude (750 nm and 100 μm).
This IR-reforming process also has certain disadvantages. IR lamps generally only heat the top sealing surface (or TSS) of a container. This means the heat must migrate through the neck finish in order to shape the inner diameter of the neck. During this heating process, the neck finish becomes deformed and can yield containers that fall outside design specifications. It is possible to manufacture specifically shaped IR lamps (round, square, etc.) for localized heating. The disadvantage of doing this is cost; custom lamps are very expensive. Lamps are also delicate, which is a major concern in a production environment. A broken lamp will result in line down time due to replacement of the lamp, will require clean up of broken glass, and could prompt product recalls should glass contaminate the product. IR lamp heating also requires relatively long cycle times and imposes high machine costs.
In summary, in order to achieve desirable tolerance levels using conventional extrusion blow molding technology, the containers typically have to undergo some type of cutting, stamping, or trimming operation. These operations have not proven to be reliable for producing the required dimensional tolerances. Nor have these operations, and others such as reforming, met the need for reduced cycle times demanded of modern, cost-effective, manufacturing processes. Another disadvantage of cutting, stamping, or trimming is the production of chips. Any packages that have been subjected to an operation that generates chips must go through a series of cleaning steps. This results in extra equipment on the line. It also results in customer complaints and product recalls in the event that all the plastic chips have not been removed from the package.
Therefore, there remains a need in the art for improved methods, apparatus, and containers that overcome the shortcomings of conventional solutions. To overcome the shortcomings of the current solutions applied to form and reform plastic containers, a new apparatus, machine, and process are provided. An object of the present invention is to decrease the cycle time (i.e., increase the speed of production output) required to manufacture plastic packages such as containers. A related object is to eliminate or at least minimize cutting, stamping, trimming, or burnishing operations. Another object is to increase the amount of plastic that can be manipulated in a practical cycle time, thereby expanding the feasible applications of the technology.
Yet another object is to decrease the cost and complexity of the machinery used to manufacture plastic packages. An additional object is to replace the IR lamps and heater bands found in the conventional solutions. It is still another object of the present invention to heat a precise area of a package very quickly so that the area can be reformed within efficient cycle times (i.e., to channel or focus the heat energy). A related object is to permit adjustment of the precise area of heating to meet the specific requirements of a particular application. Still another object is to provide an apparatus, a machine, and a method having sufficient flexibility to accommodate reforming a wide variety of containers and other plastic packages using induction heating.